Page:Popular Science Monthly Volume 3.djvu/157

Rh little explicit, as the remarks in this paper are intended for non-technical readers particularly. Now, if two strips of iron called rails are laid upon the aforesaid road, the friction is reduced sevenfold; that is to say, the same horse at the same speed could draw 7 tons, the difference between macadam and iron being as 70 lbs. to 10 lbs. This immense advantage, however, disappears when gradients have to be encountered, because the resistance due to gravity becomes so greatly in excess of the resistance due to friction, and is constant in both cases. For instance, if on a common road, up a slope of one foot in ten, the horse takes 5 cwt. in a cart over the macadam, if rails be laid down up the same hill, he could only increase the burden behind him by a little more than 1 cwt., or, in all, 6¼ cwts.; hence, in this case, the value of the rails is nearly lost. Hence the small use of tramways where hills occur.

Upon a very good macadamized road the resistance due to friction is usually taken at about one-thirtieth of the whole load carried; that is to say, if the vehicle were put upon a road sloping 1 in 30, it would just begin to move of itself. But, upon a railway, under the most favorable conditions, the resistance due to friction has been reduced to the two-hundred-and-eightieth part of the whole load carried; that is to say, the vehicle will begin to move of itself on a gradient of 1 in 280. In considering the work which a horse can perform on a tramway, it is important to bear in mind the question of speed; for, according to the experiments of Tredgold, he can draw exactly four times as much at two miles an hour as he can at five, and it appears that, at three miles an hour, he does the greatest amount of actual useful work, whereas, at ten miles an hour, only one-fourth of his actual power is available, and he cannot exert that for an hour and a half; whereas, at two and a half miles an hour, he can continue working for eight hours. Having these data before us, it is easy to compare the values of steam and horse-flesh: Suppose coals to cost in the midland districts 18s. 8d. a ton only, or one-tenth of a penny per pound, and, assuming that an average locomotive-engine will not consume more than 5 lbs. of coal in the hour per horse-power, the cost of fuel per horse-power will be a halfpenny per hour. Taking the value of the horse's provender at 1s. 9d. a day only, and supposing he works for six hours, that would cost 3½d. an hour against a halfpenny in the case of steam, or, as 7 to 1 in favor of steam; and this result is obtained on the supposition that the horse travels only at three miles an hour.

Now, to sum up the combined advantages, therefore, of an engine on a level railway against a horse on a level common road at 10 miles an hour, we shall find that the former gives an economy over the latter of nearly 300 to 1; at 5 miles an hour, it would stand as 115 to 1; and, at 2½ miles an hour, as 64 to 1.

Such are the enormous advantages of steam and rails, and with them does it not seem astonishing that better financial results have